Geotechnical Engineering Circular No. 9 Design, Analysis, and Testing of Laterally Loaded Deep Foundations that Support Transportation Facilities
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Soldier Rev B
| 3.3.5 Groundwater Conditions Groundwater conditions must be considered in the design of laterally loaded deep foundations as part of the determination of stratigraphy. Groundwater observations should be made during drilling, upon completion of drilling, and where possible, after stabilization of groundwater levels at least 24 hours or more following completion of drilling. Long-term readings are especially important when water has been used in the drilling process, either for stabilization of the borehole in soils, as part of rock coring operations, or as part of other in-situ testing or drilling operations. A detailed discussion on the measurement of groundwater levels and water pressures, as well as piezometers and groundwater observation wells, is provided in Mayne et al. (2002) and GEC 5, Geotechnical Site Characterization (Loehr et al. 2016). Groundwater conditions affect the design of deep foundations for vertical and lateral loads because they affect the effective stresses in the soil. In the specific case of analysis of lateral loads on deep foundations, some of the parameters used in lateral pile/shaft analyses have been explicitly developed for above- or below-water conditions. Therefore, the groundwater level is a critical parameter for these types of analyses. Where no groundwater data are available, an assessment of groundwater level must be made based on soil moisture descriptions, local knowledge of the site, regional geology, or other methods. In addition, assessment of the groundwater level should include consideration of flood levels, tidal and seasonal variations, and potential variations due to other sources, such as industrial operations, changes in hydrogeological conditions, etc. Where groundwater data are not available or groundwater levels may fluctuate significantly, a conservatively high groundwater level should be used to ensure that the most adverse groundwater condition has been considered in the lateral pile/shaft analysis. If necessary, a parametric study or sensitivity analysis can be performed by considering the static groundwater level and potential variations in groundwater conditions to assess the economics of designing for extreme or uncertain variations. |